Quiz 2 Flashcards
Organizing Data: Line Listing
What is line listing used for?
lecture 5
used in routine surveillance, investigating an outbreak, conducting a study, etc. to compile information in an organized manner
organized like a spreadsheet with rows and columns
Organizing Data: Line Listing
What makes up a line listing?
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row: called a record or observation
- represents one person or case of disease
column: called a variable
- contains information about one characteristic of the individuals (race or date of birth)
Organizing Data: Line Listing
What is a value?
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value of a variable is the number or descriptor that applies to a particular person (5’6”, female, never vaccinated, etc.)
- the type of values influence the way in which the variables can be summarized
can be numeric but also can be descriptive + there are four types
Organizing Data: Line Listing
What are the four types of variables?
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- nominal-scale variable
- ordinal-scale variable
- interval-scale variable
- ratio-scale variable
Organizing Data: Types of variables
nominal
define
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values are categorized without numerical ranking
(ex: ill or well, dead or alive)
Organizing Data: Types of variables
ordinal
define
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values are ranked but not necessarily evenly spaced
(ex: stages of breast cancer)
Organizing Data: Types of variables
interval
define
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measured on a scale of equally spaced units but without a true zero point (ex: shoe sizes, test scores)
Organizing Data: Types of variables
ratio
define
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an interval variable with a true zero (ex: height, age, sickness duration)
Organizing Data: Line Listing
Which variables of the 4 are qualitative variables?
also known as categorical
lecture 5
nominal and ordinal
Organizing Data: Frequency Distribution
Which variables of the 4 are quantitative variables?
also known as continuous
lecture 5
interval and ratio
Frequency Distributions
What is a frequency distribution?
lecture 5
a table or graph that shows how often different values or group of values appear in a dataset
in public health terms: a way of organizing and presenting health related data to show how often a particular health condition, behavior, or characteristic occurs in a population
- helps identify trends, risk factors, and disparities in health outcomes
Frequency Distributions
What are the features/properties of frequency distributions?
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- central location
- spread
- shape
- range
Frequency Distributions
What is the Gaussian distribution?
also known as normal distribution
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the classic symmetrical bell-shaped curve
- no skew
spread
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how widely dispersed a graph is
shape
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symmetry
can be symmetrical or asymmetrical (skewed)
Shape: Skewness
positive skew
define
central location is to the left of the tail (tail points to the right)
Shape: Skewness
negative skew
define
central location is to the right of the tail (tail points to the left)
range
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measured by spread and distribution
Frequency Distributions: Properties
central location
define
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where the graph peaks
there are three measures of central location used in epidemiology: mean, median, and mode
Central Location: Types of Measures
mean
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the average value (add up all the numbers and divide by the amount of numbers that are present)
use:
- has excellent statistical properties; commonly used in statistical manipulations and analyses
- called the center of gravity
- affected by any extreme value
Central Location: Types of Measures
median
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number in the middle (after being numerically ordered)
use:
- good descriptive measure
- relatively easy to identify
- not often used in statistical manipulations and analyses
- not generally affected by extreme values
Central Location: Types of Measures
mode
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number that shows up the most
use:
- preferred measure of central location
- can have one or two more
- used almost exclusively as a descriptive measure
- not affected by extreme values
Investigating an Outbreak
Why would we investigate an outbreak?
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- control or prevention of the health problem
- opportunity to learn / research
- public, political, or legal concerns
- public health program considerations
- training
the most important reason is for control and prevention
Investigating an Outbreak
What are the steps of an outbreak investigation?
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- prepare for field work
- establish the existence of an outbreak
- verify the diagnosis
- contruct a working case definition
- find cases systemically and record information
- perform descriptive epidemiology
- develop hypotheses
- evaluate hypotheses epidemiologically
- reconsider, refine, re-evaluate
- compare with lab and/or environment studies
- implement control and prevention measures
- initiate or maintain surveillance
- communicate findings
Investigating an Outbreak: Steps (1)
Prepare for field work
define
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officials discover an increase in the number of cases of a particular disease and then decide that a field investigation is warranted
-
scientific and investigate issues: must have the appropiate scientific knowledge, supplies, and equipment
- review applicable literature
- assemble useful references (jounrnal articles, sample questionnares)
- know what supplies/equipment to protect yourself
- have a plan of action
-
management and operational issues: must be a good manager and collaborator because most investigations are conducted by a team rather than just one individual
- roles and responsibilities for each members
- communications plan to know how often and when to calls with involved agencies, etc.
- arrange travel, lodging and local transportation
Investigating an Outbreak: Steps (2)
Establish the existence of an outbreak
define
lecture 6
verify that the cases are in fact an outbreak; observed cases compared to the number of expected cases
- outbreak or an epidemic: the occurrence of more cases of disease than expected in a given area or among a specific group of people over a particular period of time
Investigating an Outbreak: Steps (3)
Verify the diagnosis
define
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important because you must ensure that the disease has been properly identified since control measures are often disease specific and to rule out laboratory error as the basis for the increase in reported cases
- review clinical findings and lab results
- visit one or more patients with the disease to get a better understanding of clinical features
Helps with generating a hypotheses about disease spread
just like John Snow did with his investigation
Investigating an Outbreak: Steps (4)
Construct a working case defintion
define
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includes clinical criteria, and may be restricted by time, place, and person
- diagnosis may be uncertain early on in an investigation. so, cases will be classified as suspected, probable, and confirmed
Investigating an Outbreak: Steps (5)
Find cases & record information
define
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public health workers must look for additional cases to determine the true geographic extent of the problem and the populations affected by it
- passive surveillance: sending a letter describing the situation and asking for reports of similar cases (other entities report the data)
- active surveillance: telephoning or visiting the facilities by self to collect information on any additional cases
following data is collected:
- identifying information
- demographic information
- clinical information
- risk factor information
- reporter information (source of the report)
Investigating an Outbreak: Steps (6)
Perform descriptive epidemiology
define
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summarizing by time, place, and person
- provides a comprehensive characterization of the outbreak
- infer the population at risk for disease
- provides clues about source, modes of transmission, etc.
- begin thinking about where to begin intervention
helps formulate hypotheses
Investigating an Outbreak: Steps (7)
Develop hypotheses
define
lecture 6
- if the epidemic curve points to a narrow period of exposure, what events occurred around that time?
- why do these people living in one particular area have the highest rate of disease
- why are some groups at greater risk than others?
answers to these questions assist epidemiogists in formulating their hypothesis
Investigating an Outbreak: Steps (8)
Evaluate hypotheses
define
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2 ways:
1. compare hypothesis to established facts
2. use analytic epidemiology to quantify relationships:
- retrospective cohort/risk ratio
- case-cohort/odds ratio
Analytic Evaluation (Step 8)
What does a retrospective cohort study consist of?
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- small, well-defined population
- exposure and outcomes have already occurred
- calculate the attack rate for those exposed to those not exposed
- calculate risk ratio
Analytic Evaluation (Step 8)
How do you calculate the attack rate?
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attack rate = those sick who were exposed/ALL exposed
attack rate = those sick who were not exposed/ALL unexposed
high attack rate among those exposed and low attack rate among those not exposed = exposure is a strong suspect
Analytic Evaluation (Step 8)
What is the method for calculating risk ratio?
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attack rate in exposed group/attack rate in unexposed group
Analytic Evaluation (Step 8)
What does a case-cohort consist of?
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investigator asks case-patients and controls about their exposures and conducts an odds ratio to quantify the relationship between exposure and disease
controls need to be identified in this study
Analytic Evaluation (Step 8)
What is the method for calculating the odds ratio?
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(number of exposed cases x number of unexposed controls) / (number of exposed controls x number of unexposed cases)
or
(AxD)/(BxC)
Statistical significance
Why is statistical significance important?
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implies that the association between the exposure and disease did not happen by chance
Investigating an Outbreak: Steps (9)
Reconsider, refine, re-evaluate
define
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done in the case that analytic studies do not provide adequate insight
Investigating an Outbreak: Steps (10)
Compare - lab & environmental
define
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laboratory evidence can confirm the findings
environmental studies can explain why an outbreak occurred
Investigating an Outbreak: Steps (11)
Control & prevention
define
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primary goal: to control outbreak AND prevent additional cases
control measure are usally aimed at segments of the chain of transmission (agent, host, mode of transmission, portal of entry)
Investigating an Outbreak: Steps (12)
Initiate / maintain surveillance
define
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once control and prevention measures are implemented, they must be monitored
- this usually comes in the form of active surveillance
questions epidemiologists ask:
- are new cases slowing down or stopping
- are new cases continuing to occur
- where are the new cases, if any
- has the outbreak spread outside the original area where interventions were targeted
Investigating an Outbreak: Steps (13)
Communicate findings
define
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oral briefing for local authorities
- in attendance: local health authorities, those responsible for implementing control and prevention measures (epidemiologists)
- investigator describes what they found and recommendations for action
written report
- the usual format (intro, background, methods, etc…)
- this may serve as a reference for health departments encountering a similar outbreak in the future
